Radiation cured coatings

ABSTRACT

A time and labour saving multiple coating system for porous substrates which involves the application of a mono or poly isocyanate catalysed UV curable acrylate composition in such circumstances as to penetrate at least part of the surface of the substrate, at least a partial surface curing of the applied composition prior to any substantial degree of self curing, and thereafter applying (whether subsequent to any sanding or not) a further surfacing composition which preferably also is an acrylate composition that is both self curing and UV curable.

The present invention relates to UV cured coatings.

UV cured coatings are almost 100% solids and are cost effectivealternatives to the less environmentally friendly two pack polyurethanesthat have been traditionally used in wet wall linings. Such coatings areknown to rely on activation by a mercury vapour lamp to cause photoinitiators in the coating to release free radicals. The free radicalsinteract with unsaturated monomer and resin causing them to polymeriseinto a solid cured film.

When panels such as fibre cement are coated it is difficult to achievegood adhesion between a UV cured primer and the fibre cement panel. Thisis because the fibre cement is porous and the UV curable coating soaksinto the surface where the UV emissions cannot reach. This means thatthe UV primer cannot be properly cured.

The present invention addresses regimes of coating a substrate(preferably having at least some surface porosity) which neverthelessallow the advantages to be derived from a UV cured coating to beretained while at the same time ensuring appropriate adhesion betweenany chosen substrate and the sequence of coatings thereon.

The present invention also addresses such coated substrates as well asapparatus and related means and methods applicable thereto. In oneaspect the invention consists in a method of coating a substrate(preferably having at least some surface porosity), said methodcomprising the steps of

(I) at least applying to the surface of the substrate a mono or polyisocyanate catalysed UV or other radiation (hereinafter "UV") curableacrylate composition by means of

(i) serial application of

(a) a liquid carried substantially solvent free mono or poly isocyanatecatalyst, and

(b) the UV curable acrylate composition, or

(ii) an application of a mixture of a substantially solvent free mono orpoly isocyanate catalyst and the acrylate composition;

(II) photo curing at least the surface of the coating applied as (I);

(III) optionally, mechanically treating the cured surface resulting from(II);

(IV) applying to the surface resulting from (II) or (III)

(i) a UV curable composition, and/or

(ii) serially

(a) a liquid carried substantially solvent free mono or poly isocyanatecatalyst, and

(b) a UV curable acrylate composition, and/or

(iii) a mixture of a substantially solvent free mono or poly isocyanatecatalyst and the acrylate composition; and

(V) photo curing at least the surface of the coating(s) applied as (IV).

Preferably said substrate has a porous surface.

Preferably said substrate is of a fibre cement, e.g., Portland based.

Preferably said catalyst of step (I) is a diisocyanate.

Preferably said diisocyanate is aromatic or aliphatic.

Preferably said diisocyanate is polymethylene.

In other forms the catalyst is any catalyst of general formulaR--(N═C═O)n where R is an organic moiety and n is any integer 1 orgreater.

Preferably said catalyst is carried by a non solvent i.e., for the R--N═C═O!n! organic compound or composition.

Preferably said liquid carried catalyst is carried by a monomer.

In some forms step (I) comprises the application of plural catalysed andUV curable acrylate coatings, the first being by means of one of (I)(i)and (I)(ii), and the second, the same or different, being by means ofone of (I)(i) and (I)(ii).

Preferably said photo curing is with UV light. In less preferred formsany other activating radiation can be used (e.g., gamma).

Preferably step (III) is performed.

Preferably step (III) is or includes sanding (with or without washing).

Preferably where step (IV)(i) is used the UV curable composition is anacrylate composition or compound. Preferably where step (IV)(ii) is used

said catalyst is a diisocyanate or as otherwise defined in respect ofstep (I) and/or

said UV curable acrylate composition is as defined in respect of step(I) or otherwise.

Preferably where step (IV)(iii) is used the catalyst and acrylatecomposition are as defined in respect of step (I) or otherwise.

Preferably only one of steps (IV)(i), (ii) or (iii) are used, or onlytwo thereof.

In other forms a step (VI) follows which comprisesthe application of atleast one compatible coating over the cured layer of (V), the coating(s)of the substrate by steps (I) through (V) priming the substrate.

Step (VI) may include mechanical and/or chemical treatments to modifysurface appearance and/or characteristics.

Preferably said substrate is a panel of fibre cement.

In some forms said substrate includes some free water inclusions.

In still a further aspect the invention consists in a coated substratecomprising

(A) a substrate having some surface porosity,

(B) below and at least partly above the surface of the substrate of amono or poly isocyanate catalysed or UV light catalysed acrylatecomposition, the regions further into the substrate being more mono orpoly isocyanate catalysed than at or above the substrate surface, and,conversely, the at or above surface regions being more UV light curedthan the regions further into the substrate, and

(C) at least one (at least primarily) UV cured acrylate coating on thecured composition of (B).

In still a further aspect the present invention consists in a method ofcoating a substrate, said method comprising at least the steps of

(I) at least applying to the surface of the substrate a mono or polyisocyanate catalysed UV or other radiation (hereinafter "UV") curableacrylate composition which is also self curing by means of

(i) serial application of

(a) a liquid carried substantially solvent free mono or poly isocyanatecatalyst, and

(b) the UV curable acrylate composition, or

(ii)an application of a mixture of a substantially solvent free mono orpoly isocayanate catalyst and the acrylate composition;

the application by (I)(i) or (ii) providing a composition having from2.5 to about 10% v/v of the catalyst,

(II) photo curing at least to a substantial extent at least the surfaceof the coating applied as (I) prior to any substantial degree of selfcuring;

(III) "sanding" the cured surface resulting from (II);

(IV) applying to the surface resulting from (III)

(i) a UV curable composition, and/or

(ii) serially

(a) a liquid carried substantially solvent free mono or poly isocyanatecatalyst, and

(b) a UV curable acrylate composition, and/or

(iii) a mixture of a substantially solvent free mono or poly isocyanatecatalyst and the acrylate composition; and

(V) allowing the curing of or curing (optionally photocuring) at leastthe surface of the coating(s) applied as (IV).

In still a further aspect the present invention consists in a method ofcoating a substrate, said method comprising at least the steps of

(I) at least applying to the surface of the substrate a mono or polyisocyanate catalysed UV or other radiation (hereinafter "UV") curableacrylate composition which is also self curing by means of

(i) serial application of

(a) a liquid carried substantially solvent free mono or poly isocyanatecatalyst, and

(b) the UV curable acrylate composition, or

(ii) an application of a mixture of a substantially solvent free mono orpoly isocyanate catalyst and the acrylate composition;

the application by (I)(i) or (ii) providing a composition having fromabout 15 to about 30% v/v of the catalyst,

(II) photo curing at least to a substantial extent at least the surfaceof the coating applied as (I) prior to any substantial degree of selfcuring,

(III) applying to the surface resulting from (II)

(i) a UV curable composition, and/or

(ii) serially

(a) a liquid carried substantially solvent free mono or poly isocyanatecatalyst, and

(b) a UV curable acrylate composition, and/or

(iii) a mixture of a substantially solvent free mono or poly isocyanatecatalyst and the acrylate composition; and

(VI) allowing the curing of or curing (optionally by photocuring) atleast the surface of the coating(s) applied as (III).

Preferably where any of the steps (I), (II), (III), (IV) and (V) arepresent, they are performed on a production line at a line speed of from5 to 30 m/min.

Preferably step (I) results in an application of composition at a rateof from 5 to 50 gsm.

Preferably when the layer of step (I) is not subjected to a "sanding"step the catalyst content is lower in the outer layer(s).

In yet a further aspect the invention consists in apparatus forperforming the method of the present invention, said apparatuscomprising

(I) means to apply a composition or composition components to asubstrate in accordance with step (I),

(II) means to photo cure as in step (II) the coated substrate of step(I),

(III) optional, means to mechanically treat the at least partially curedcoated substrate of step (II),

(IV) means to apply to the surface resulting from step (II) or step(III) a composition or composition components as required by step (IV),and

(V) optional, means to photo cure the coating(s) of step (IV).

The invention involves as an option, a method of coating panelsespecially building panels comprising preparing a face of the panel by

(a) applying to said face a coating of an aromatic or aliphaticisocyanate; or the latter blended with a UV curable primer,

(b) applying a primer over the isocyanate coat, said primer containing amonomer, a photo initiator and optionally a higher molecular weightresin, and

(c) exposing the primer coat to UV radiation to cause the primer topolymerise into at least a substantially surface cured coat.

To those skilled in the art to which the invention relates, many changesin construction and widely differing embodiments and applications of theinvention will suggest themselves without departing from the scope ofthe invention as defined in the appended claims. The disclosures and thedescriptions herein are purely illustrative and are not intended to bein any sense limiting.

The invention consists in the foregoing and also envisages constructionsof which the following give examples.

The panel faces may be coated by spraying, curtain coating or rolling.The isocyanate may be R--N═C═O where R is an aryl, diaryl or aliphaticgroup. The compound may be a diisocyanate. The aliphatic group may be alower alkyl. The aliphatic group may be polyethylene. The isocyanate ispreferably a high solids, film forming preparation. The primer maycontain aqueous suspensions of monomer and a photo initiator.

Optionally a primer resin may be present to give the coat increaseddensity. Pigment may also be present. The purpose of this coat is likeall primers, to establish high initial adhesion to the substrate so thatsubsequent coats achieve reliable intercoat adhesion. Preferably thecoats are applied at 5-50 gsm preferably 20-30 gsm and ambienttemperature.

This process works better if the substrate has some porosity with eitherwater content or --OH groups. Manufactured boards are suitable with afibre content, including fibrocement.

In a following stage (D) the primer may be exposed to UV light in orderto activate the photo initiators in primer. The free radicals releasedthereby are free to cross link the monomers and promote curing. If theisocyanate coat has not occluded the substrate surface the primer layermay penetrate the substrate where the monomers are free to link with theisocyanate coat. The unreacted isocyanate groups from the initial coatare free to link with the monomers in the second coat.

Boards may be sold in this condition, namely primed. Alternatively theboards may proceed to top coating or other finishing.

Fibrocement sheets 2400×1200 mm are used to line wet areas such asabattoirs, showers, spray booths and industrial work places. We havesucceeded in coating them with a production line consisting of a seriesof coating stations with a throughput speed of 5 to 30 m/min (e.g., 10m/min) using the following stages:

Stage 1

The first station has a 50 inch wide driven applicator 4 roll whichcreates a nip with the station work surface 6. The applicator issupplied with a Bayer hexamethylene diisocyanate available as DESMODUR N3400 at a rate which deposits 10 gsm. The panel progresses to station 2where infra red lamps 8 dry the coat which sinks into the panel surfaceand combines with moisture in the panel and any free --OH in the panelsurface.

Stage 2

The panel progresses to the third station where a drive/applicatorroller 10 deposits 5 to 30 gsm of a non-pigmented acrylic primercontaining monomer, high mol. wt. Resins and photo initiators. Theapplicator roller feeds the panel and applies the primer to the drypanel.

Stage 3

The primed panel is transferred to a station where an array of UV lampsare switched on exposing the whole panel surface for a few seconds.

Stage 4

The panel receives a second coat of primer at a feed station where thefeed direction is contrary to the roll applicator direction. Thisapplicator is intended to fill the voids in the panel surface.Application rates fall to 5-10 gsm.

Stage 5

The panel receives UV cured sanding primer coat at 15 to 30 gsm followedby UV exposure as described above. Feeding through a fine grit (180 to320, e.g., #220) belt sander is then necessary to prepare the coatedpanel for finishing coats. Pigmented primers are used in alternativeprocesses.

A preferred fibrocement is that of James Hardie Building ProductsLimited of Auckland, New Zealand marked as HARDIFLEX™. It is a flatmedium density cellulose reinforced autoclaved cement sheet produced ona Hatschek machine followed by autoclave curing.

A hardboard substrated suitable is that of Fletcher Wood Panels Limitedof Auckland, New Zealand which their technical information sheet"Hardboard" defines as an oil tempered high density wood fibre panel.

The process is also effective when used on other suitably preparedsubstrates, e.g., timber, fibreboard, cement board, other wood basedproducts and metal.

We have found the advantages of the above procedure/example:

1 Superior adhesion between the initial coat and the substrate.

2 Superior adhesion between intermediate coats.

3 Cross linking between the UV curable coat and initial coat.

4 Labour cost and handling are reduced.

5 Environmentally much more friendly.

BRIEF DESCRIPTION OF THE DRAWINGS

The aforementioned procedure of the present invention will now bedescribed in more detail and with different preferments and/or optionswith reference to the following drawings in which

FIG. 1 is a diagram of an apparatus as depicted in the drawingaccompanying the provisional specification of our New Zealand PatentApplication 286219,

FIG. 2 is a preferred flow diagram at least to a surface preparationstage which lends itself to following surface treatments (i.e., FIG. 2showing details of a preferred method of operation in relation to thepreparation of fibre cement sheet),

FIG. 3 is a variation of the procedure of FIG. 2,

FIG. 4 shows a third option for fibre cement,

FIG. 5 shows a preferred option for coating plywood to provide a shutterpanel (i.e., where the substrate is plywood),

FIG. 6 is a variant of the procedure of FIG. 5 where the product is aFIG. 7 shows and the substrate is plywood,

FIG. 7 shows a flow diagram involving a two coat operation only wherethe substrate is plywood and the output product is a shutter panel,

FIG. 8 is a further procedure where the substrate is plywood and theoutput product is a shutter panel system,

FIG. 9 is still a further variant where the substrate is plywood and theoutput product is a shutter panel system,

FIG. 10 is still a further variant flow diagram where the substrate isplywood and the output product is a shutter panel system, this timethere being a one coat followed by a sanding and then a one coat finishapplication,

FIG. 11 shows still a further flow arrangement where the substrate isplywood and the output product is a shutter panel system,

FIG. 12 is a flow diagram suitable for an oil tempered hardboard wherethe substrate is any one or more of medium density fibre board, particleboard, BISON™ board, a wood veneer, a plywood, oriented stand board,etc., and

FIG. 13 is another option for oil tempered hardboard where the substrateis as stated in relation to FIG. 12.

Satisfactory output products are provided by any of the procedures setout in FIGS. 2 through 13 irrespective of whether or not the operatingsequence includes any, some or all of the apparatus shown in FIG. 1, thedrawing which accompanied the provisional specification of our NewZealand Patent Application 286219.

In respect of the procedures of each of FIGS. 2 through 13, thepreferred line speeds are in the ranges stated, namely from 5-30 metersper minute feed and the ranges of application in grams per square meterare in the ranges stated in the drawings (i.e., 5/10 means a range offrom 5 to 10). References such as 5/30% in the Examples hereof mean arange of from 5 to 30% volume/volume of the component.

In respect of the choice of materials for the sequences of FIGS. 2through 13 the following are applicable with each example being apreferment only and then only in respect of options. Each provided asuccessful outcome.

EXAMPLE 1

UV paint FLEXIPRIME™ (Whitehall) 100% solids UV convertible urethaneacrylic with 5/30% v/v catalyst and the balance being UV convertibleurethane acrylate (such as sourced from Whitehall Technical ServicesLimited of South Auckland, New Zealand). FLEXIPRIME™ is a UV cure primerand top coat system for products requiring good flexibility and not atthe expense of chemical and weather resistance. Its viscosity isapproximately 20 poise and its solids are 100% UV convertibleurethane-acrylic. Recommended cures are 15 meters/min. under a 300 wattmercury tube. FLEXITOP™ (Whitehall) can be made gloss or satin.

Preferred cross linkers (variously referred to herein throughout as thekey, the catalyst, linker or the like) include a catalyst available fromBayer AG under any of the codes N34, N32, N75, N100, N37 or LS2102.

In the following examples in each instance the cross linker, linker, keyor catalyst is one also available from Bayer AG and has the codes given.

EXAMPLE 2

UV paint FLEXIPRIME™ 100% solids UV convertible urethane acrylic with5/30% v/v (N34, N32, N100, N37 or LS2102).

EXAMPLE 3

Operation 2--Coat with: N34, N32, N75, N100, N37 or LS2102.

Operation 3--Coat with FLEXIPRIME™ UV convertible urethane acrylic withno cross linker.

EXAMPLE 4

FLEXITOP™ 100% solid convertible urethane with 5/30% v/v cross linker(N34, N32, N75, N100, N37 or LS2102).

EXAMPLE 5

FLEXITOP™ 100% solid convertible urethane with 5/30% v/v cross linker(N34, N32, N75, N100, N37 or LS2102).

EXAMPLE 6

FLEXITOP™ 100% solid convertible urethane with 5/30% v/v cross linker(N34, N32, N75, N100, N37 or LS2102).

EXAMPLE 7

FLEXITOP™ 100% solid convertible urethane with 5/30% v/v cross linker(N34, N32, N75, N100, N37 or LS2102).

EXAMPLE 8

FLEXITOP™ 100% solid convertible urethane with 5/30% v/v cross linker(N34, N32, N75, N100, N37 or LS2102).

EXAMPLE 9

FLEXITOP™ 100% solid convertible urethane with 5/30% v/v cross linker(N34, N32, N75, N100, N37 or LS2102).

EXAMPLE 10

FLEXITOP™ 100% solid convertible urethane with cross linker N34, N32,N75, N100, N37 or LS2102 5/30% cross linker.

EXAMPLE 11

UV paint FLEXIPRIME™ solids UV convertible urethane acrylic+cross linker5/30% N34, N32, N75, N100, N37 or LS2102

EXAMPLE 12

UV paint FLEXIPRIME™ solids UV convertible urethane acrylic+cross linker5/30% v/v (N34, N32, N75, N100, N37 or LS2102).

From experimentation with the foregoing systems we have found from about2.5 to 10% v/v of the cross-linker will yield a sandable surface.

From about 15 to 30% v/v cross linker can be used if perfect intercoatadhesion without sanding is required.

In this case a subsequent in-line coat is needed to give immediatestackability without risk of set-off. This is the preferred system to gounder an opaque UV-urethane topcoat.

Pot-life is reduced to about a day once cross linker is mixed in.

The advantages of such systems become apparent by comparing:

(A) CONVENTIONAL PAINT PROCESS

1) Substrate arrives on site.

2) Edges are dusted and painted white.

3) Surface is primed using a curtain coater.

4) Product is racked and stored for 10/14 days.

5) Product is sanded and dusted.

6) Product is top coated.

7) Product is racked and cured for seven days at ambient temperature.

8) Product is graded and wrapped.

9) Produce is dispatched.

Process takes 3-4 weeks and uses a labour force of twenty men andadministration staff, and

(B) DUAL CURE UV SYSTEM OF PRESENT INVENTION

1) Product arrives on site.

2) Product is edge dusted and edges painted white.

3) Product is loaded on to UV line for priming, sanding and top coating.

4) Product is graded and dispatched.

Process takes 0.5 days and employs five men and same administrationstaff.

I claim:
 1. A method of coating a substrate selected from the groupconsisting of fibrocement and fiber cement, said method comprising atleast the steps of(I) at least applying to the surface of the substratea mono or poly isocyanate catalysed radiation curable acrylatecomposition which is also self curing by means of(i) serial applicationof(a) a liquid carried solvent free mono or poly isocyanate catalyst,and (b) the radiation curable acrylate composition, or (ii) anapplication of a mixture of a solvent free mono or poly isocyanatecatalyst and the acrylate composition;the application by (I) (i) or (ii)providing a composition having from about 15 to about 30% v/v of thecatalyst, (II) photo curing at least the surface of the coating appliedas (I) prior to any self curing (III) applying to the surface resultingfrom (II)(i) a radiation curable composition, and/or (ii) serially(a) aliquid carried solvent free mono or poly isocyanate catalyst, and (b) aradiation curable acrylate composition, and/or (iii) a mixture of asolvent free mono or poly isocyanate catalyst and the acrylatecomposition; and (IV) curing at least the surface of the coating(s)applied as (III).
 2. The method of claim 1, wherein the substrate isfibrocement.
 3. The method of claim 2, wherein any of the steps (I),(II), (III) and (IV) are performed on a production line at a line speedof from 5 to 30 m/min.
 4. The method of claim 2, wherein step (I)results in an application of composition at a rate of from 5 to 50 gramsper square meter.
 5. The method of claim 1, wherein the curing in step(IV) is photo curing.
 6. The method of claim 1, wherein said catalyst ofstep (I) is diisocyanate.
 7. The method of claim 6, wherein saiddiisocyanate is aromatic or aliphatic.
 8. The method of claim 6, whereinsaid diisocyanate is polymethylene.
 9. The method of claim 6, whereinthe catalyst is any catalyst of general formula R--(N═C═O)n, where R isan organic moiety and n is any integer 1 or greater.
 10. The method ofclaim 1, wherein step (I) comprises the application of plural catalysedand radiation curable acrylate coatings, the first being by means of oneof (I) (i) and (I) (ii), and the second, the same or different, being bymeans of one of (I) (i) and (I) (ii).
 11. The method of claim 1, whereinsaid photo curing is with ultraviolet spectrum light.
 12. The method ofclaim 1, wherein step (III) (i) is used and the radiation curablecomposition is an acrylate composition or compound.
 13. The method ofclaim 1, wherein step (III)(ii) is used andsaid catalyst is adiisocyanate.
 14. The method of claim 1, wherein step (III)(iii) is usedand the catalyst and acrylate composition provide a composition havingabout 15 to about 30 % v/v of the catalyst.
 15. The method of claim 1,wherein only one of steps (III)(i), (ii) or (iii) are used.
 16. Themethod of claim 1, wherein two of the steps (III)(i), (III)(ii) and(III)(iii) are used.
 17. The method of claim 1, further comprising astep (V), after step (IV), which comprises applying at least onecompatible coating over the coating applied as (IV), wherein the coating(s) of steps (I) through (IV) have primed the substrate.
 18. The methodof claim 17, wherein step (V) includes mechanical and/or chemicaltreatments to modify surface appearance and/or characteristics.
 19. Themethod of claim 1, wherein said substrate includes free waterinclusions.
 20. The method of claim 1, wherein the radiation curableacrylate composition is UV radiation curable.